This invention pertains generally to the field of battery condition monitoring and management.
Batteries and battery stacks are utilized in many applications such as telecommunication power supplies, electric vehicles, uninterruptible power supplies, and photovoltaic systems. In such systems, the battery or batteries either provide the main power supply for the system or back up a primary power supply. Although batteries are relied on to carry out these vital roles, they are a significant source of system failure because of the inevitably limited battery lifetime and reduced reliability as the battery ages. Because batteries are such a crucial factor in overall system reliability, many industrial and vehicle applications for batteries utilize continuous monitoring of the condition of the batteries to detect impending battery failure and to allow replacement or recharging of the battery before failure occurs.
Battery monitoring devices have been used to track and log battery performance parameters such as battery output voltage, current, temperature, state of charge, and remaining capacity. Low power battery packs, such as those used in portable devices, are often equipped with advanced monitoring and management systems to improve battery reliability and alert users to possible problems. However, systems of the type utilized for low power batteries are not generally suitable for heavy industrial battery applications as such monitoring systems tend to be relatively complex and costly, and generally require a relatively clean and controlled environment. There is thus a significant need for simple and cost effective battery monitoring systems for industrial battery applications.
Most of the present battery-monitoring devices incorporate real-time data acquisition systems that continually monitor the battery terminal conditions. Because of the large volume of real-time data obtained from the battery, the logged data is normally transmitted from the battery monitor to other larger devices, such as general purpose computers (e.g., PCs) or programmable logic controllers (PLCs). These devices are programmed to categorize and save the data as well as to alert users to potential problems. A large volume of data thus must be transferred from the battery monitor over a communications link to a PC or other device that is saving or analyzing the data. Such systems are not suitable for industrial battery applications, primarily because continuous real-time data logging requires a very large on-board data storage capability for the data monitors. On the other hand, continuous communication of the data generated by the monitor to a peripheral device is generally not feasible because of cost and the mode of battery use. For example, in motive power applications, the battery is on a mobile truck or vehicle, and a communications link with a stationary peripheral (e.g., a wireless communication link) is complex and expensive. In addition, due to the limited amount of on-board storage available, the rate at which data is sampled for storage is necessarily lower than would otherwise be desired. The decreased sampling rate impacts the quality of the logged data and its usefulness, as users can miss significant battery events (e.g., voltage and current spikes). Further considerations include the cost and size of monitors. Price and size constraints for mobile battery systems, in particular, limit the amount of allowable on-board memory, which is a significant component of the overall monitor volume and cost. The resulting compromises required for conventional battery monitoring thus result in the end users obtaining less data than desired, and the data that is acquired may not include significant short-term events.
The present invention carries out activity-based battery data-logging with only a minimal requirement for data memory capacity. Rather than recording every data point (e.g., voltage, current, temperature of the battery), the invention monitors battery activity in terms of charge, discharge, and open circuit events. Although battery parameters are preferably sampled at very high sampling rates, only a relatively small number of memory data fields are stored and updated. When the onset of an event is detected, i.e., a change of state to charge, discharge, or open circuit (no current flow), a new data record is created which is composed of a selected number of data fields. At every sampling instant, the data fields are preferably updated based on various decision criteria. When the event ends (a change of state occurs), the record for that event is closed, and a new record is initiated for the succeeding event. The entire event, which may last from a few seconds or fractions of a second to several hours, is summarized in a single record characterizing the battery activity during the entire event.
Battery monitoring apparatus in accordance with the invention includes a voltage sense input port, current sense input port and an output communications port through which data may be communicated. A programmable microcontroller is connected to the voltage sense and current sense input ports to receive signals therefrom and to the output communications port to at least transmit signals thereto, and is also connected to provide data to and from a non-volatile memory. The voltage sense input port is connected to leads which extend to a battery to sense the voltage across the battery, and the current sense input port is connected to leads extending to a current sensor which provides a signal representing the current through the battery. The microcontroller is programmed to monitor the signal from the current sense input port to detect a change in battery state between battery charging, discharging and open circuit. A battery event is defined between changes of state. During each event, the battery voltage and current is monitored and the microcontroller stores data to the non-volatile memory after an event which includes at least the time of the event and the total current over time as supplied from or to the battery during the event. At selective times, the microcontroller transfers data from the non-volatile memory through the output communications port to a computer for analysis and/or display to an operator. The apparatus may also include a temperature sense input port, connectable to a temperature sensor at the battery. The microcontroller receives a signal from the temperature sense input port during a battery event and stores data to the non-volatile memory after an event corresponding to one or more of the maximum temperature and minimum temperature occurring during the event.
In addition to data fields including the time of the event and the total current over time (amp-hours), the microcontroller may also store fields corresponding to the state of the event and the total current over time supplied to or from the battery, data fields corresponding to event alarms for over-voltage, current or temperature, maximum event voltage, maximum event voltage time, minimum event voltage, minimum event voltage time, maximum event temperature, maximum event temperature time, maximum event current, and maximum event current time. Although an event (a battery state between changes of state) may last for hours, only one data field record need be saved per event, greatly minimizing the memory requirements for the non-volatile memory while preserving the quality and relevance of the data that is saved. Furthermore, very fast sampling rates can be utilized to ensure that transient events such as maximum voltages and currents will be detected and the characteristics and timing of these events will be stored for later analysis.
The invention may also include a current sensor having a shunt connected in series with the battery through which flows the current flowing through the battery, an amplifier connected to receive the voltage across the shunt, a filter to low pass filter the signal from the amplifier, and an analog to digital converter to receive the filtered output signal from the amplifier and provide digital output data on a digital data communications link to the current sense input port, thereby providing a digital data signal to the monitoring apparatus to minimize noise in the signal. The current sensor can include a high gain amplifier and a low gain amplifier, each of which is connected to receive the voltage across the shunt, with the analog to digital converter including a first channel connected to receive the output from the high gain amplifier and a second channel to receive the output from the low gain amplifier. The microcontroller is programmed to selectively receive the current sense data from the first analog to digital converter channel when the current being sensed is below a threshold value and from the second analog to digital converter channel when the current being sensed is above a threshold value.
The microcontroller may also be programmed to store one or more data fields for each battery event to the non-volatile memory from other stationary data fields such as installation time, high voltage setpoint, low voltage setpoint, high current setpoint and high temperature setpoint, which can be compared to the data being read to trigger alarms, a cycle counter, total hours of open circuit overall events, total hours of discharge overall events, total hours of charge overall events, total amp-hours of discharge overall events, total amp-hours of charge overall events, and a count of the number of events recorded.
Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.